Processes for utilisation of purified coal compositions as a chemical and thermal feedstock and cleaner burning fuel

ABSTRACT

Processes for upgrading of a coal product and preparing of a purified coal product are provided. The process comprises the steps of: (i) providing a purified coal composition, wherein the composition is in the form of solid particles, and wherein at least about 90% by volume (% vol) of the solid particles are no greater than about 500 μm in diameter; and (ii) combining the purified coal composition with a solid coal feedstock, in order to create a combined solid-solid blend upgraded coal product.

FIELD OF THE INVENTION

The invention is in the field of processing and utilisation of solidhydrocarbons, most particularly coal. In particular the invention is inthe field of remediation and exploitation of waste coal fines derivedfrom mineral extraction and mining activities.

BACKGROUND OF THE INVENTION

Coal mines, especially multi-seam surface mines and associated coalprocessing and preparation plants, are limited in output and marketpricing by the availability of high grade quality seams necessary tomeet high specifications for coking and pulverised coal injection (PCI)coals. These limitations are leading to lower and less efficientproduction of this important chemical feedstock from a rapidlydiminishing worldwide resource base. Tighter product specifications forinternationally traded thermal coals are also leading to lower, and lessefficient, production in the coal industry. As a result of moredemanding environmental standards, coal processing plants areincreasingly also limited in their ability to store waste coal productin tailings ponds, impoundments or tips.

Thermal coals sold and traded internationally for power generation, aretypically high ash content (at least 15-20% m dry basis), high sulphurcontent (1-2% m dry basis), moderately-high water content (10-15% m orhigher) and with a relatively coarse particle size distribution (<50mm). Coal power plant boilers utilise pulverised PCI fuel (i.e. driedcoal particles, typically in the size range 20-120 μm) and consumesignificant amounts of energy in crushing, drying and pulverisingthermal coals. The ash generated during combustion has to be removedeither as slag ash or fly ash: in both cases ash reduces operationalefficiency and incurs environmental as well as commercial costs fordisposal. Power stations utilise flue gas desulphurisation techniques tominimise the emissions of sulphur oxides to the atmosphere; the cost ofoperating such desulphurisation techniques is proportional to the coalfeedstock sulphur content.

Coal seams with high ash content are abundant worldwide, from numerousgeological reserves, sometimes as thick seams persisting over a widegeographical area, but many are not exploitable economically due to theproblems described above.

Coal fines and ultrafines, including microfines, are the small particlesof coal generated from larger lumps of coal during the mining andpreparation process. While coal fines retain the same energy potentialof coal they are generally considered a waste product as the particulatenature of the product renders it difficult to market and transport. Asmuch as 70-90 million tonnes of coal fines are produced in the US aloneas waste bi-product every year by the mining industry (Baruva, P.,Losses in the coal supply chain, IEA Clean Coal Centre Rep.CCC/212, p.26, December 2012, ISBN 978-92-9029-532-7), the vast majority of whichis left unused. Coal fines are therefore generally discarded as spoilclose to the colliery forming large waste heaps or contained in largeponds that require careful future management in order to avoidenvironmental contamination.

Nevertheless, coal fines could offer the potential for a cheap andplentiful supply of hydrocarbons particularly rich in carbon (M. Lewitt,Opportunities for fine coal utilisation, IEA Clean Coal Centre Rep.CCC/185, July 2011, ISBN 978-92-9029-505-1.). However, in its naturalstate, coal fines typically contain significant levels of ash-formingcomponents and water that render it unsuitable for many conventionaluses. The traditional view has been that the cost of dewatering and/ordrying as well as de-ashing fines <150 μm in diameter generally exceedsthe actual fuel value of the resultant product (Muzenda, E., Potentialuses of South African Coal Fines: A Review, 3rd International Conferenceon Mechanical, Electronics and Mechatronics Engineering (ICMEME'2014)Mar. 19-20, 2014 Abu Dhabi (UAE), p. 37). It is known to add highlyprocessed coal fines to fuel oils in order to reduce the cost per unitvolume of the resultant blended fuel oil (see for example U.S. Pat. No.9,777,235). In addition, highly processed coal fines can be added tocrude oil in order to contribute to the fractionation products followingdistillation (see International Patent Application Published asWO2017/174973). In both instances the coal fines are blended with aliquid hydrocarbon to create a resultant admixture with enhancedperceived commercial value greater than that of the solid fines alone.

Commercial processes have been developed to convert coal waste fines(<500 microns) and ultrafines (<150 microns) into coal pellets, e.g.Coal Tech coal agglomeration technology in South Africa(http://www.coaltechenergy.com/). Another example (U.S. Pat. No.5,242,470 A) claims coal particles in a mixture with a top particle sizeof about 28 mesh (700 microns) with at least about 50 percent of theparticles being smaller than about 48 mesh (300 microns) with surfacemoisture content of 2-20% and 14-24% by weight. Note that total moistureis the sum of the surface moisture and inherent, pore-held internalmoisture which itself can range from 1% m to 10% m for bituminous coals.These processes retain some water to aid the pelletising process, but donot upgrade coal waste in terms of ash content which is typically in therange 30-50% m, nor do they reduce the particle size.

Coal waste fines slurry has been to lower ash (i.e. <10% m) via frothflotation and have partially removed moisture to <20% m to form a coalpowder using ultrafine particles (https://mineralsrefining.com/ andLuttrell, G. Yoon, R-H et al., Hydrophobic-hydrophilic separation (HHS)process for the recovery and dewatering of ultrafine coal,https://mineralsrefining.com/wp-content/uploads/2015/09/SME-2016-Gupta-et-al-HHS-Process-a.pdf).Others (US Patent Application 20160082446) operate at coarser particlesizes, i.e. <750 microns. A common feature in all these approaches isthe utilisation of fines slurry as available in situ with only thecoarsest particles removed. They lack a clear product quality target forutilisation, in terms of mineral matter content (assessed as ashcontent), particle size distribution and moisture content. Furthermore,such approaches have been driven mainly by the resource characteristicswith little or no consideration being given to the importance of millingto the optimum coal particle size which will enable mineral matter to bereleased during froth flotation separation and achieve appropriatelevels of ash content, particle size and moisture content for productutilisation in the power sector.

Coal rank and maceral composition (microscopically recognisable,individual organic constituents of coal) are key additional propertiesfor coking coal utilisation assessment. Froth flotation techniques canlead to some concentration of the more valuable vitrinite maceral (U.S.Pat. No. 8,591,607 B2), but this is largely adventitious, small inmagnitude, and not exploited in practice.

Now that international trading of coals is well established, theselection of coals for use in power generation no longer simply dependson the quality that can be produced at the nearest mines. Powergenerating companies recognise that coal quality significantly affectspower plant variable costs, consequently Fuel Evaluation Tools have beendeveloped to provide the basis behind the transfer price agreement withcoal traders (Coal and Biomass Characterisation for a Power Generator,Uniper Technologies, Nottingham, UK, Coal Research Forum, ImperialCollege London, 20 Apr. 2016. http://www.coalresearchforum.org/CRF%202016ICL/W%20Quick,%20Uniper,%20ICL,%2020-04-16.pdf).

Blending of coals to optimise economic and technical considerations isnow more common than the utilisation of coal from a single mine or coalprocessing plant (Tilman, D. A., Duong, D. N. B. and Harding, N. S,Solid Fuel Blending, Elsevier, 2012. ISBN 978-0-12-380932-2). Designingthe optimum coal blend is influenced by the need to optimiseenvironmental impact from emissions, efficiency, maintenance andavailability, reagents and by-products and this is assessed from therange of coal quality parameters used in international trading coalspecifications.

Coals are blended at the coal-mine, preparation plant, trans-shipmentpoint or at the customer power station or coke oven. The blending methodselected depends on site conditions, level of blending, quantity to bestored and blended, the accuracy required and the end use of the blendedcoal. Typically in power stations the stacking method with a fullymechanised system is followed (Sloss, L. L., Blending of coals to meetpower station requirements, Report ref. CCC/238, IEA Clean Coal Centre,London, July 2014, ISBN 978-92-9029-559-4).

Coals are not just used in fuels. They represent a prime source ofcarbon for various metallurgical and chemical processes. The worldwideshortage of prime coking coals available for the chemical process ofmetallurgical coke manufacture drives the need to include morenon-traditional components in coking coal blends. (Obayashi, Y., andSheldrick, A., Japan steelmakers scramble for coking coal to make upDebbie losses, Reuters Business News, 21 Apr. 2017,http://uk.reuters.com/article/uk-japan-steel-shortage/japan-steelmakers-scramble-for-coking-coal-to-make-up-debbie-losses-idUKKBN17N16J,and Bounds, A., Global demand for coking coal set to revive Cumbriamining, Financial Times, 19 Jun. 2017,https://www.ft.com/content/b054c570-528e-11e7-bfb8-997009366969). Hence,there is a demand for high quality reagents for use in steel andaluminium making that cannot be satisfied solely using traditionalsources of metallurgical coke.

The present invention addresses the problems that exist in the priorart, not least in reducing the further accumulation of waste fines as abi-product of the coal mining industry.

SUMMARY OF THE INVENTION

The present inventors have developed a process that provides for theutilisation of very high quality (low ash, sulphur and water content)purified coal products, that may be pelleted or briquetted, that havebeen upgraded from waste from coal tailings ponds, impoundments or tipsand reject materials from current coal production processing (e.g.thickener underflow or tailings underflow waste streams), as well ashigh-ash content inferior seam coal, hitherto not exploitableeconomically.

The purified coal product shows utility in the following exemplarynon-limiting applications:

-   -   as a blend component for coal production processing, designed to        upgrade mined coal quality to meet specification requirements        for use;    -   as chemical feedstock (coking coal for metallurgical coke        manufacture or pulverised coal injection [PCI] into blast        furnaces for steel production);        -   for power generation;        -   for thermal industrial or domestic utilisation;        -   as a stand-alone product for any of these uses; and    -   as a blend component, or stand-alone feed at a power plant,        designed to improve operational efficiency, reduce sulphur        oxide, particulate and trace element emissions, reduce carbon        dioxide emissions per unit energy produced and reduce fuel cost.

Accordingly, in a first aspect the invention provides a process forupgrading of a coal product comprising the steps of:

-   -   (i) providing a purified coal composition, wherein the        composition is in the form of solid particles, and wherein at        least about 90% by volume (% vol) of the solid particles are no        greater than about 500 μm in diameter; and        -   (ii) combining the purified coal composition with a solid            coal feedstock, in order to create a combined solid-solid            blend upgraded coal product.

In a specific embodiment, the purified coal composition is formed intopellets comprised of the solid particles. The purified coal compositionis comprised within purified coal pellets that comprise in per cent massof the total product (% m) at most about 12% m ash, optionally less than8% m ash, suitably less than 5% m ash.

According to one embodiment the purified coal pellets comprise at mostabout 25% m water, optionally less than 20% m of water, suitably lessthan 10% m of water, typically less than 2% m of water. Suitably, thePCPs comprise at most about 3% m of total sulphur and, optionally atmost about 0.1% m chlorine, suitably at most about 0.05% m chlorine.

Typically, the purified coal composition is comprised within purifiedcoal pellets that comprise total sulphur contents amounting to at mostthe native organic sulphur content plus no more than 0.5% m ofadditional mineral sulphur.

According to one embodiment, the solid coal feedstock is selected fromone or more of the group consisting of: coking coal; pulverised coalinjection coal (PCI); thermal coal and coal pulverised feed.

In a specific embodiment of the invention, the combined solid-solidblend comprises at most about any one of: 1% m, 5% m, 10% m, 20% m, 30%m, 40% m, 50%, and 60% m of the purified coal composition based on thetotal mass of the combined solid-solid blend, with the balance comprisedof solid coal feedstock from single or multiple sources.

In a specific embodiment of the invention the combined solid-solid blendcomprises at least about 0.01% m and at most about 60% m of the purifiedcoal composition, with the balance comprised of solid coal feedstockfrom a single source based on the total mass of the combined solid-solidblend.

In yet a further embodiment of the invention the combined solid-solidblend comprises at least about 0.01% m and at most about 60% m of thepurified coal composition, with the balance comprised of solid coalfeedstock from multiple sources based on the total mass of the combinedsolid-solid blend.

In a second aspect the invention provides a process for upgrading of acoal product comprising the steps of:

-   -   a) providing a first purified coal composition from a first        source of coal fines, wherein the composition is in the form of        solid particles that are compacted into pellets, and wherein at        least about 90% by volume (% vol) of the solid particles are no        greater than about 500 μm in diameter;    -   b) providing a second purified coal composition from a second        source of coal fines different from the first source, wherein        the second composition is in the form of solid particles that        are compacted into pellets, and wherein at least about 90% by        volume (% vol) of the solid particles are no greater than about        500 μm in diameter; and    -   c) combining the first and second compositions in order to        create a combined solid-solid pelletized blended upgraded coal        product.

According to further embodiments of the invention the combinedsolid-solid blend upgraded coal product of any of the aforementionedaspects and embodiments comprises one or more of:

-   -   at least about 1% m, 2% m, 3% m and 4% m; and at most about 6%        m, 7% m, 8% m and 10% m ash; and    -   at least about 0.1% m, 0.2% m and; at most about 0.5% m, 1.5% m,        3% m, and 5% m of additional mineral sulphur above the native        organic sulphur content; and    -   at least about 2% m, 3% m or 4% m; and at most about 9% m, 10%        m, 11% m, 12% or 13% m water;    -   based on the total mass of the product.

In a specific embodiment of the invention the purified coal compositionis subjected to a de-watering step prior to step (i) of combining thepurified coal composition with the solid coal feedstock.

In a specific embodiment of the invention the purified coal compositionis subjected to an ash removal step prior to step (i) of combining thepurified coal composition with the solid coal feedstock.

A third aspect of the invention provides for a blended coal productcomprising a purified coal composition in combination with a solid coalfeedstock, wherein the purified coal composition is in the form ofparticles and is further characterised in that at least 95% by volume (%v) of the purified coal composition particles are no greater than about500 μm in diameter, and wherein the blended coal product comprises atmost about 99% mof purified coal composition, based on the total weightof the blended coal product. In a specific embodiment of the inventionthe blended coal product comprises a purified coal composition in whichtypically at least 95% v, optionally at least 98% v, and suitably atleast 99% v of the particles are no greater than about 250 μm,optionally no greater than 100 μm, in diameter.

In embodiments of the invention a blended coal product is providedcomprising a purified coal composition in combination with a solid coalfeedstock, wherein the purified coal composition is in the form ofparticles and is further characterised in that at least 95% v,optionally at least 99% v, of the particles are no greater than about250 μm, suitably 100 μm, typically 20 μm in diameter.

A fourth aspect the invention provides a process for preparation of apurified coal product, the process comprising the steps of:

-   -   a. obtaining a starting material that comprises coal;    -   b. subjecting the starting material to at least one fine        grinding stage so as to reduce the starting material to a        particulate composition in which substantially all of the        particles are no more than 500 microns (pm) in diameter;    -   c. exposing the particulate composition to at least one froth        flotation stage so as to separate hydrocarbonaceous material        comprised within the particulate composition from mineral        matter, wherein during the at least one froth flotation stage        the hydrocarbonaceous material is associated with froth produced        and separated from the at least one froth flotation stage;    -   d. washing the froth separated from the at least one froth        flotation stage with water to release the hydrocarbonaceous        material; and    -   e. subjecting the hydrocarbonaceous material to at least one        dewatering stage so as to obtain a particulate purified coal        product that has an ash content of less than 12% m, a water        content of less than 25% m and wherein the particles comprised        within the particulate purified coal product have a d90 of less        than 70 μm.

In a specific embodiment of the invention the starting materialcomprises a feedstock selected from one or more of the group consistingof: waste from coal tailings ponds, impoundments or tips; rejectmaterials from coal production processing; and high-ash content inferiorseam coal.

According to a further embodiment the fine grinding stage is conductedin a ball or bead mill. Typically the starting material is processedduring find grinding stage to a particulate composition in whichsubstantially all of the particles are no more than 250 μm. 150 μm, 100μm, 90 μm and; suitably no more than 80 μm in diameter; optionally nomore than 70 μm in diameter.

In a particular embodiment of the invention the froth flotation stage isconducted with solids to liquids loading of less than 20% m, suitablyless than 15% m, typically less than 10% m and optionally less than 5% mor lower.

In yet a further embodiment the dewatering stage comprises subjectingthe hydrocarbonaceous material to dewatering selected from one or moreof the group consisting of: mechanical dewatering; cyclonic dewatering;centrifugal dewatering; and thermal dewatering. Optionally thedewatering stage may comprise subjecting the hydrocarbonaceous materialto at least two different dewatering stages.

According to one embodiment of the invention the particulate purifiedcoal product obtained by the process has an ash content of less than 12%m or 8% m, optionally less than 5% m, typically less than 2% m, suitablyless than 1% m. In a further embodiment the particulate purified coalproduct obtained by the process has a water content of less than 25m %or 20 m %, typically 15% m, suitably less than 12% m, optionally lessthan 10% m, typically less than 8% m. In embodiments the particlescomprised within the particulate purified coal product have a d90 ofless than 100 μm or 70 μm, typically 50 pm, suitably less than 40 μm,optionally less than 20 μm.

A fifth aspect of the invention provides a particulate purified coalproduct obtainable by a process as described herein, wherein theparticulate purified coal product has an ash content of <2% m, typically<1% m, a water content of <7% m and wherein the particles comprisedwithin the particulate purified coal product have a d90 of less than 70μm, typically less than 50 μm. Typically, the particulate coal productof is formed into a briquette.

A sixth aspect of the invention provides for a pelletized coal productcomprising a purified coal composition, wherein the purified coalcomposition is in the form of micronized particles, wherein the productcomprises:

-   -   at most about 0.5% m, 1% m, 2% m, 3% m and 4% m of ash; and    -   at most about 0.1% m, 0.2% m, and 0.5% m of additional mineral        sulphur above the native organic sulphur content;    -   at most about 5% m, 8% m, 12% m, 15% and 20% m water;    -   based on the total mass of the product; and

further characterised in that at least 95% by volume (% v) of thepurified coal composition particles are no greater than about 500 μm indiameter. In a specific embodiment of the invention the pelletized coalproduct comprises a purified coal composition in which typically atleast 97% v, optionally at least 98% v, and suitably at least 99% v ofthe particles are no greater than about 250 μm, optionally no greaterthan 100 μm, in diameter. It will be appreciated that the invention maybe subjected to further combinations of the features disclosed hereinbut which are not explicitly recited above.

DRAWINGS

The invention is further illustrated by reference to the accompanyingdrawings in which:

FIG. 1 shows schematic diagrams of typical blending operations utilisingpurified coal product pellets (called PCP pellets) at (a) coal-minepreparation plant A, (b) port B, and (c) power plant C and coke oven D.

FIG. 2 shows (a) simulated sieve analysis of fragments from impact testson PCP pellets for three different guar gum concentrations of 7.5% m,4.0% m and 1.6% m (b) water uptake results for PCP pellets for threedifferent guar gum concentrations of 7.5% m, 4.0% m and 1.6% m.

FIG. 3 shows a graph of calculated net power efficiency in a Germancoal-fired power plant by way of comparison between the blended coalproduct (referred to as purified coal product—PCP) is compared toreference coals from a variety of countries.

FIG. 4 shows a flow diagram of a process of one embodiment of thepresent invention.

FIG. 5 shows a flow diagram of a process of a further embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

All references cited herein are incorporated by reference in theirentirety. Unless otherwise defined, all technical and scientific termsused herein have the same meaning as commonly understood by one ofordinary skill in the art to which this invention belongs.

Prior to setting forth the invention in greater detail, a number ofdefinitions are provided that will assist in the understanding of theinvention.

As used herein, the term “comprising” means any of the recited elementsare necessarily included and other elements may optionally be includedas well. “Consisting essentially of” means any recited elements arenecessarily included, elements that would materially affect the basicand novel characteristics of the listed elements are excluded, and otherelements may optionally be included. “Consisting of” means that allelements other than those listed are excluded. Embodiments defined byeach of these terms are within the scope of this invention.

The term “coal” is used herein to denote readily combustible sedimentarymineral-derived solid hydrocarbonaceous material including, but notlimited to, hard coal, such as anthracite; bituminous coal;sub-bituminous coal; and brown coal including lignite (as defined in ISO11760:2005). “Native” or “feedstock” coal refers coal that has not beensubjected to extensive processing and comprises a physical composition(e.g. maceral content) that is substantially unchanged from the point ofextraction. In contrast, the terms “coal-derived product”, “coalreplacement product” and “purified coal compositions” are used herein torefer to various coals which have been subjected to one or moreprocesses that lead to a change in physical and/or chemical compositionsof the coal such that it is substantially changed from the point ofextraction—i.e the natural state.

As used herein, the term “ash” refers to the inorganic—e.g.non-hydrocarbon—mineral component found within most types of fossilfuel, especially that found in coal. Ash is comprised within the solidresidue that remains following combustion of coal, sometimes referred toas fly ash. As the source and type of coal is highly variable, so is thecomposition and chemistry of the ash. However, typical ash contentincludes several oxides, such as silicon dioxide, calcium oxide, iron(III) oxide and aluminium oxide. Depending on its source, coal mayfurther include in trace amounts one or more substances that may becomprised within the subsequent ash, such as arsenic, beryllium, boron,cadmium, chromium, cobalt, lead, manganese, mercury, molybdenum,selenium, strontium, thallium, and vanadium.

As used herein the term “low ash coal” refer to native coal that has aproportion of ash-forming components that is lower when compared toother industry standard coals. Typically, a low ash native or feedstockcoal will comprise less than around 12% m ash. The term “deashed coal”,or the related term “demineralised coal”, is used herein to refer tocoal that has a reduced proportion of inorganic minerals compared to itsnatural native state. Ash content may be determined by proximateanalysis of a coal composition as described in ASTM D3174-12 StandardTest Method for Ash in the Analysis Sample of Coal and Coke from Coal.In embodiments of the present invention ash content in purified coalproduct of less than 10% m, less than 8% m, less than 5% m and less than2% m or even less than 1% m are obtained. Indeed, the present inventorshave found quite unexpectedly that products having very low ash contentsof around or below 1% m can be obtained from starting material that isas much as 50% m ash without having to sacrifice yield levels thatrender the process un-commercial.

Inferior coal is a term used in geological survey of the quality of coalseams (e.g. UK coal survey, 1937) and refers to intrinsic ash in coalbands or coal seams above 15.1% m and below 40.0% m. Coal bands or coalseams consisting of inferior coal contain mineral matter intimatelymixed within the coal itself and consequently are very difficult topurify using conventional coal processing techniques.

As used herein, the term “coal fines” refers to coal in particulate formwith a maximum particle size typically less than 1.0 mm. The term “coalultrafines” or “ultrafine coal” or “ultrafines” refers to coal with amaximum particle size typically less than 0.5 mm (500 microns (μm),approximately 0.02 inches). The term “coal microfines” or “microfinecoal” or “microfines” refers to coal with a maximum particle sizetypically less than 20 μm.

Most suitably the particle size of the coal fines that is utilised asfeedstock may be at most 1000 μm or 500 μm. More suitably, the maximumparticle size may be at most 300 μm, 250 μm, 200 μm, 150 μm, or 100 μm.

A typical measure of particle size is to quote a maximum particle sizeand a percentage value or “d” value for the proportion by volume ofparticles within the sample that fall below that particle size.Suitably, the “d” value associated with any of the above maximumparticle sizes may be d99, d98, d95, d90, d80, d70, d60, or d50.

Most suitably, the maximum particle size cut-off for purified coalproduct produced by the process of the invention may be at most 95 μm,90 μm, 85 μm, 80 μm, 75 μm, 60 μm, 50 μm, 40 μm, 30 μm, 20 μm, 18 μm, 15μm, 12 μm, 10 μm, or 5 μm. The minimum particle size may be 0.01 μm, 0.1μm, 0.5 μm, 1 μm, 2 μm, 3 μm, or 5 μm. Any “d” value may be associatedwith any one of these particle sizes. To maximize the desirable physicaland chemical properties of the purified coal product it is typical forthe product particle size to be both relatively homogeneous and small.For instance, in a specific embodiment of the invention the purifiedcoal product has a d90 of <100 μm, <90 μm, <70 μm, <50 μm optionally <20μm. Suitably, the microfine purified coal product has a d99 of <70 μm,<60 μm, <50 μm, <40 μm, <20 μm, and optionally <10 μm.

As used herein, the term “water content” refers to the total amount ofwater within a sample, and is expressed as a concentration or as a masspercentage (% m). When the term refers to the water content in a coalsample it includes the inherent or residual water content of the coal,and any water or moisture that has been absorbed from the environment.As used herein the term “dewatered coal” refers to coal that has anabsolute proportion of water that is lower than that of its naturalstate. The term “dewatered coal” may also be used to refer to coal thathas a low naturally-occurring proportion of water. Water content may bedetermined by analysis of a native or purified coal composition asdescribed in ASTM D3302/D3302M-17 Standard Test Method for TotalMoisture in Coal.

The term “hydrocarbonaceous material” as used herein refers to amaterial containing hydrocarbons; hydrocarbons being an organic compoundconsisting substantially of the elements hydrogen and carbon.Hydrocarbonaceous material may comprise aliphatic as well as aromatichydrocarbons.

As used herein, the terms “native organic sulphur content” of coal andother hydrocarbonaceous materials refers to the sulphur content presentin the organic molecular structure, typically as thiol, thioether,thiophene and other aromatic sulphur heterocyclic species. In general,organic sulphur cannot be removed by physical processing methods, onlyby chemical processes, such as hydrogenation and hydrocracking. It ismeasured indirectly as the difference between total sulphur content andthe mineral sulphur species that comprise pyrite, free sulphur andsulphate (ASTM D2492-02 (2012) Standard Test Method for Forms of Sulfurin Coal). The processes of the present invention may show utility indepleting mineral sulphur species from a hydrocarbonaceous startingmaterial, such as a high or medium sulphur coal.

Coal mines, especially multi-seam surface mines and associated coalprocessing and preparation plants, are limited in output and marketpricing by the availability of high grade quality seams necessary tomeet high specifications for coking and pulverised coal injection (PCI)coals. These limitations are leading to lower and less efficientproduction of this important chemical feedstock from a rapidlydiminishing worldwide resource base. Tighter product specifications forinternationally traded thermal coals are also leading to lower, and lessefficient, production in the coal industry. As a result of moredemanding environmental standards, coal processing plants areincreasingly also limited in their ability to store waste coal productin tailings ponds, impoundments or tips.

Thermal coals sold and traded internationally for power generation, aretypically high ash content (at least 15-20% m dry basis), high sulphurcontent (1-2% m dry basis or more), moderately-high water content(10-15% m or higher) and with a relatively coarse particle sizedistribution (<50 mm). Coal power plant boilers utilise pulverised PCIfuel (i.e. dried coal particles, typically in the size range 20-120microns) and consume significant amounts of energy in crushing, dryingand pulverising thermal coals. The ash generated during combustion hasto be removed either as slag ash or fly ash: in both cases ash reducesoperational efficiency and incurs environmental as well as commercialcosts for disposal. Power stations utilise flue gas desulphurisationtechniques to minimise the emissions of sulphur oxides to theatmosphere; the cost of operating such desulphurisation techniques isproportional to the coal feedstock sulphur content.

Coal seams with high ash content are abundant worldwide, sometimes asthick seams persisting over a wide area, but a great many are notexploitable economically due to the problems described above.

In one embodiment, the present inventors utilise a purified coal productin methods and processes that blend the purified coal product withotherwise off-spec, low or intermediate grade coal feedstock, in orderto produce a coal product that falls within the rigorous standardsrequired for thermal and/or coking and PCI coals. Suitably, the purifiedcoal product may be comprised within a pelletized coal product, suchthat blending with native feedstock coal involves combining apredetermined mass of pellets with a predetermined mass of nativefeedstock coal to produce a blended product. The relative proportions ofthe starting materials (e.g. pellets and feedstock) can be decided basedupon the desired final chemical and physical properties of the blendedproduct. By way of non-limiting example, a low-grade feedstock-coal maybe upgraded to a desired specification by determining how much of thepelletized purified coal product needs to be added, in order to achieverequired ash, water, sulphur and/or chlorine content. In this way thepurified coal product can serve as an additive (when as a minorfraction) or as a blend component (when present as a major fraction) ofthe final coal product.

Purified coal pellets derived from coal waste sources, such as thickenerunderflow, impoundments, tailings ponds or tips, and from inferior coalseams otherwise not economically extractable, can now be manufactured tosuch high quality (very low ash, moisture, sulphur and phosphoruscontents with Gross Calorific Value in excess of 5500 kcal/kg, asreceived basis and in some cases, coking properties as well) such thatthey can be blended to:

-   -   a. achieve specification limits used for internationally sales        of:        -   i. metallurgical coking coals of high value and scarcity;        -   ii. pulverised coal injection (PCI) coals of intermediate            value; and        -   iii. thermal coals.    -   b. enable coal processing plants to increase total production,        improve production efficiency and extend the lifetime of the        mine by utilising the beneficial properties of PCP to include        lower quality coal seams or other coals;    -   c. enable coal processing plants to minimise price penalties by        utilising the beneficial properties of PCP to offset shortfalls        in specifications from normal coal production.

The purified coal pellets may be prepared by several process stages:

-   -   milling, to reduce particle size sufficiently to enable        efficient separation;    -   froth flotation in aqueous media to separate coal from mineral        matter;    -   filtration under pressure and air-blowing to remove water by        mechanical means;    -   compaction into pellets to provide mechanical integrity; and    -   drying thermally to reduce water to below 5% m

Blending purified coal pellets into coking coal, PCI coal and thermalcoal production processing streams improve the final product quality forsome, or all, of the following parameters needed to achieve marketspecifications, minimise penalties from shortfalls in suchspecifications, and enable coal processing plants to include lowerquality streams, thus increasing production or extending mine lifetime.

Typically to achieve the aims of bringing blended coal products up tothe required specifications it is necessary to ensure the product meetsa number of established parameters. Reduction of content of ash, and/ormoisture, and/or phosphorus, and/or sulphur, and/or carbon, and/orsodium oxide in the ash is a key requirement, in order to reduce wasteand improve energy efficiency. It is also desirable to increase indicesof calorific value, and/or swelling, and/or dilatation, and/or fluidityin the final blended product. Finally, the blended products shouldachieve targets for volatile matter content, and/or petrographiccomposition, and/or grindability, and/or coke strength reactivity.

According to specific embodiments of the invention, the processes andmethods of the invention may take place at any of the followinglocations in the supply chain:

-   -   at the mine        -   by selective stacking and recovery of different quality            products from stockpiles        -   by blending on belts or into the train load out bin with            product stockpiles of different specifications;    -   at a port stockyard by blending truck or train loads on receipt        into stockpiles designated for ship arrivals;    -   during ship loading by blending varying quantities from        different stockpiles; and    -   at a customer stockyard by blending from different stockpiles        fed by truck, train or ship.

In one embodiment of the invention blending purified coal pellets intocoal pulveriser feed contributes to combustion plant efficiencyimprovements and cost reductions during a steam raising process forpower or heat generation.

Key benefits that become apparent as a result of the products andprocesses of the present invention, are set out in more detail below.

Reduced Delivery Costs:

Reducing the ash and moisture content of a typical hard coal results inPCP with approximately 25% higher energy density than an equivalenttraded coal. This translates directly into a 25% saving in deliverycosts through the supply chain. Coal handleability describes the abilityof the bulk coal to flow through chutes and bunkers or transfer betweenconveyors and so on. The two most important parameters affecting flowcharacteristics are free moisture and fines content; in both cases highvalues, especially in combination, can lead to coal that is verydifficult to handle. In severe cases, coal can become stuck in railwagons or coal bunkers and considerable time and effort is required toclear blockages. The PCP is effectively 100% coal fines, and it is onlyby forming pellets that the coal can be efficiently handled. Thehandleability of purified coal pellets is likely to be different to thatof coal. In fact, uniform sized coal pellets would normally be expectedto exhibit superior flow characteristics to that of native feedstockcoal.

Reduced Grinding Energy During Grinding Feed Coal to Pulverised Fuel(PF) Particle Sizes:

The ease with which a coal can be milled is commonly measured as theHardgrove Grindability Index (HGI). Traded coals typically have HGI inthe range 45-65, with low numbers indicating a coal that is difficultgrind. Testing on PCP has shown HGI values of 67 and 74, which areequivalent to an easy-to-grind coal. In fact, because the pre-pelletizedcoal particle size distribution is similar to that required aftermilling traded coal, it is evident that relatively little energy isrequired to produce pulverised coal from PCP, or blends comprising PCP,in a power plant.

Less Preheating of Inlet Air to the Grinding Mill:

To dry coal before it is delivered to the boiler the primary combustionair is typically pre-heated. At this point 70% of the moisture in thecoal is evaporated, resulting in pulverised fuel (PF) with ˜3% moisturecontent. This is dry enough for PF to flow freely through pipelines tothe boiler. Mill inlet air temperatures vary from 150-400° C., dependingon mill design and coal moisture. However, PCP already has very lowmoisture content, so there is no need to dry the fuel further,consequently the air inlet temperature to the mill can be reducedaccordingly. Mill inlet temperatures between 140-180° C. are requiredfor South African, Australian and Indian coals to dry the coalsufficiently, whereas PCP, and blends that comprise significantproportions of PCP, requires far lower mill inlet temperatures. For a100% PCP composition a reduced inlet temperature of only 79° C. isrequired.

Improved Combustion Efficiency:

Coal combustion has two stages: devolatilisation occurs rapidly (<0.1seconds) while the resulting char takes many seconds to burn out, as ittravels through the boiler. Combustion efficiency describes how much ofthe heat content of the coal is combusted within the boiler. For atraded coal there is an efficiency loss from about 1% unburned carbonefficiency loss. Faster burn out is obtained by using smaller coalparticles. The PF size distribution when firing PCP is considerablybetter than seen when firing standard coals. In particular embodiments,it is likely that the percentage of particles above 150 μm in diameterwill be less than 5% and therefore very high combustion efficiencies arepossible when firing PCP and PCP-containing blends.

Greater Boiler Efficiency:

The largest boiler efficiency loss in a power plant is the heat lost inthe flue gases, which typically exit the air-heaters at around 130° C.The heat lost in moisture in the flue gases will be lower for PCP, sincethere is only approximately 2% moisture in the pellet. Also heat lostwithin the ash is lower for PCP than for standard native coal, althoughthis is a relatively smaller effect.

Reduced Slagging and Fouling:

The deposition of fused ash deposits is known as slagging and causesloss of boiler availability; it is associated with coals containing highlevels of iron or calcium. High sulphur US coals are known to beespecially prone to slagging because they also contain high levels ofiron. PCP has a very low slagging risk because it contains very lowlevels of iron, calcium and sodium in the ash. Ash deposition in theback-end zones of the boiler or air-heater is known as fouling. US highsulphur coal also shows higher risks for air-heater fouling than PCP.

Reduced Corrosion:

The corrosion of water boiler walls is related to elevated levels ofchlorine in coal, especially when combined with high levels of alkalimetals. Sulphur in coal also increases the risk of corrosion, but to alesser extent than chlorine. US high sulphur coals pose the highest riskfor boiler corrosion, due to their high sulphur and chlorine content.Corrosion risks are greatly reduced for PCP, and PCP containing blends,because the production process is removes a high proportion of thechlorine content and the levels of alkali metals are also slightlyreduced.

Reduced Risk of Premature Boiler Tube Failure from Erosion:

Such erosion is caused by the flow of abrasive ash past the tubes. Thisrisk is dependent on the quantity and abrasiveness of the coal ash andflue gas velocities. It is an especially significant problem in Indianpower plants because Indian coals contain very high levels of abrasiveash, and Indian power plants firing indigenous coals typically have tobe specially adapted to manage erosion risks. Such erosion risks arereduced significantly by the lower coal ash level of PCP, and PCPcontaining blends, leading to a significant increase in plantavailability.

Lower Amounts of Furnace Bottom Ash and Pulverised Fuel Ash:

Reducing the ash content of coal obviously results in lower amounts offurnace bottom ash and pulverised fuel ash produced as by-products. PCPand PCP containing blends inherently produce less ash. This isbeneficial to those power plants with insufficient local market to sellthe ash, for cement manufacture usually, who otherwise would incurcommercial cost and cause environmental problems disposing of the wasteash.

Lower Carbon Content in Ash Sold for Use in Cement:

As mentioned, wherever possible power plants aim to sell ash to externalcompanies to avoid incurring costs for disposal. The most common use ofcoal ash is as a cement replacement material in the manufacture ofconcrete. In Europe the standard EN450 stipulates quality requirementsthat must be achieved to qualify for this market; the most critical ofthese is carbon-in-ash levels should be <5% to meet a ‘Grade A’standard. Carbon-in-ash is a function of combustion efficiency and coalash content. The improved combustion efficiency observed for PCP, andPCP containing blends, means that low carbon-in-ash levels areachievable. Such that what little ash is produced is also of greatereconomic value.

Reduced Flue Gas Desulphurisation Costs:

Sulphur oxides emission limits at most coal-fired power plants are lowerthan levels produced during combustion, so Flue Gas Desulphurisation(FGD) technology is commonly installed. The most common variant of thisis limestone-gypsum FGD, whereby flue gases are mixed with a limestone(CaCO₃) slurry and gypsum (CaSO₄.2H₂O) is produced as a by-product. PCPhas low sulphur content and reducing coal sulphur content has a linearimpact on SO₂ emissions, so less limestone is required for the FGDprocess, which reduces expenditure on reagents. In addition, FGDconsumes considerable amounts of power and has substantial maintenancedemands, both of which will be reduced when operating with PCP.

Lower Emissions of Carbon Dioxide:

CO₂ emissions are directly related to the quantity of carbon burned, anda 1% increase in absolute unit efficiency will lead to a 2.5% reductionin CO₂ emissions (for a 40% efficient coal power plant). PCP and PCPcontaining blends provide significant reductions in CO₂ emissions, dueto lower fuel moisture content and higher unit operating efficiency. Forthe German hard coal power plant modelled in the Examples below andshown in FIG. 1 , CO₂ emissions are predicted to be 5% lower for PCPthan for the US high sulphur coal. Of this 5% reduction, approximately3.5% is from the lower CO₂ emission intensity of PCP as a fuel and 1.5%is due to the higher plant efficiency.

Reductions in Auxiliary Power Consumption:

Auxiliary power is electricity used within the power plant for theoperation of mills, fans and pumps etc. Typically, around 5-8% ofelectricity produced at a power plant is consumed as auxiliary power andis therefore not available for export to the power grid. PCP can deliversignificant reductions in auxiliary power consumption as a direct resultof all of the ancillary benefits so far described. In particular, thepre-milled state of PCP and blends containing PCP results in lowerprocessing power and handling demands for the fuel and waste ash.

In one embodiment the invention provides for a blended coal product thatis derived, in part, from low grade coal but that is suitable for use incoking, pulverised coal injection (PCI) and thermal coal products forinland and international trade. The blended coal product is an upgradedcoal product that permits use of otherwise uneconomical grades of coalfor uses that would otherwise be restricted only to high grades. Suchuses include as feed for metallurgical coke plants, blast furnaces,coal-fired power stations and industrial coal-fired heating plants.

A coal stockpile at a terminal, port or mine has three main functions:

-   -   Buffering by providing sufficient reserve of blended raw        materials to guarantee the continuous operation of the truck        loading, ship loading and processing plant.    -   Integration of several raw coal feeds with different chemical        and/or physical characteristics in such weight proportions that        a completed pile represents the requisite composition.    -   Homogenising by spreading out each feed in many layers over the        full length of the pile, thus differences in chemical or        physical material properties in cross-sections of the pile        compared with the average of the property in the input of the        pile are minimised.

Three examples of typical blending operations are describedschematically in FIGS. 1(a), (b) and (c).

-   -   a. At a coal mine preparation plant, where stockpiles of raw        coal from several seams (four in this case) are blended at a        preparation plant close to mine A. PCP plant A constructed        nearby would process current waste (thickener underflow) from        mine A coal preparation plant and historical waste from the        tailings pond (s) into PCP. The PCP would be fed on to a moving        conveyor belt from a track hopper or wagon to merge with a        washed coal stream from the coal preparation plant (which may        not meet the full trading specifications required); the        resultant blended washed coal would meet the trading        specifications.    -   b. At a port stockyard, where stockpiles of washed coal are        received by road, rail or barge from several coal preparation        plants (four in this case at port B) and mixed in a blending        stockpile. PCP is also transported from a PCP plant to the port        typically by road, rail or barge and stored, preferably in a        covered hopper, silo or storage vessel to minimise moisture        uptake from rain water. PCP may be mixed on to a blending        stockpile using conventional stackers which stack individual        washed coals in layers, and reclaimers before being loaded on to        a ship for export. Alternatively, conventional conveyor blending        on a moving belt where PCP is fed on to the belt from a track        hopper or wagon to merge with the blend of washed coals from the        stockpile. In this way a blend from washed coals 5, 6, 7 and 8        could be upgraded to meet international trading specifications.        Stackers pile bulk material such as coal or PCP on to a        stockpile, whereas a reclaimer can be used to recover the        material. They normally travel on a rail between stockpiles in        the stockyard.    -   c. At a power plant or coking plant, where stockpiles of washed        coal are received by road, rail or barge from several        consignments from ships, by rail, road or barge (four        consignments in this case at power plant C or coke oven D) and        mixed in a blending stockpile. PCP is also transported to the        plant by road, rail, ship or barge and stored, preferably in a        covered hopper or storage vessel to minimise moisture uptake        from rain water. PCP may either be mixed with a blending        stockpile using conventional stackers and reclaimers or via        conveyor belt blending before being either dried and pulverised        prior to combustion in utility boiler C or loaded as a charge in        coke oven D. In this way a blend from washed coals 9, 10, 11 and        12 could be upgraded to meet an optimised blend either to        improve the operational efficiency of the utility boiler C or        the quality of the metallurgical coke produced at coke oven D.

Suitable blending equipment to mix purified coal pellets with otherfeeds within coal preparation plants, and within both coal-fired powerplants and industrial boilers, include stackers, reclaimers, feeders andconveyors. Suitable manufacturers include ThyssenKrupp Robins, Inc.,6400 South Fiddlers Green Circle, Suite 700, Greewood Village, Colo.80111-4985, USA, Bedeschi Mid-West Conveyor, 8245 Nieman Road, Lenexa,Kans. 66214, USA., Feeco Int., 3913 Algoma Road, Green Bay, Wis.54311-9707 USA, Nepean, 23 Graham Hill Road, Narellan, NSW 2567Australia, and FLSmidth, Vigerslev Allé 77, 2500 Valby, Denmark.

In a further embodiment of the invention, a blended product is providedwhich comprises a first PCP derived from a first native coal source incombination with at least a second PCP derived from a second native coalsource different from the first native coal source. Optionally, at leastthe first native coal source comprises a low-grade coal. Suitably thesecond native coal source comprises a coal of higher grade compared tothe first native coal source. In an alternative embodiment, both thefirst and second native coal sources are low grade coal sources.Typically, the first and/or second native coal sources comprise wastecoal fines, such as those present in pond tailings or processing plantthickener underflow.

The invention further provides for the use of a PCP as an additive forreducing one or more of the group consisting of: ash content;carbon-in-ash content; sulphur content; and chlorine content in a coalfeedstock.

The present invention further provides for the use of a PCP as anadditive for increasing the combustion efficiency in a coal feedstock.

In embodiments of the invention the process for preparation of amicronized PCP is provided. As set out in FIG. 4 , a process is providedin which a feedstock starting material (10) is subjected to one or morefine milling stages (20). The starting material (10) is typicallyselected from residual coal discard such as low-grade material, wastematerial, production underflow and such like. Whilst the startingmaterial (10) comprises hydrocarbonaceous material that is ofpotentially high value, it may comprise considerable amounts of ash,sulphur and water rendering it of limited use for conventional purposes.The one or more fine milling stages (20) convert the highlyheterogeneous starting material (10) into a finely ground producttypically having a d100 of at most around 100 μm. The finely groundproduct is subjected to at least one froth flotation step (30) which isused to sort hydrophobic hydrocarbonaceous material within the coal fromthe hydrophilic mineral materials that constitute the ash. Followingseparation of the ash from the hydrocarbonaceous materials, the purifiedmicrofine coal material comprised within the froth is washed extensively(40) with water. The resultant purified coal product material isdewatered (50) using one or more processes that may include mechanical,thermal and/or rotational drying techniques (50). Reduction of watercontent to below 10% m is preferred, optionally less than 5% m can beobtained, and typically water content of below 2% m is achievedaccording to embodiments of the invention. The micronized purified coalproduct (60) may be maintained in powdered state or may be subjected toadditional processing whereby it is combined with binding agents thatfacilitate pelletization or briquette formation. Alternatively, thepurified coal product (60) may be combined with a liquid hydrocarbon,such as a refined or unrefined oil (e.g. residual fuel oil, diesel orcrude oil), in order to form a slurry that may be stored or pumped toother locations.

A process according to embodiments of the invention is set out in FIG. 5that provides for multiple coal fine grinding steps (20, 21) as well asmultiple froth washing (40, 41) and de watering (50, 51) steps in orderto produce purified coal product meeting a desired specification. In theembodiment shown in FIG. 5 , coal milling stages (20, 21) include afirst pass grind to obtain a product having d100 of at most around 100μm, followed by a second grinding stage to obtain a finer product havinga d80 of around 5 μm which is then passed to the flotation step (30).Multiple volumes of water are utilised in order to wash the frothextensively (40,41) prior to de-watering steps (50, 51). A combinationof membrane filter pressing together with centrifugal or cyclonicdrying, as well as thermal treatment enables suitable dewatering tooccur in order to meet the required low water content thresholds thatare characteristic of micronized purified coal products of embodimentsof the invention (60).

The invention is further illustrated by reference to the followingnon-limiting examples.

EXAMPLES

Demineralising and dewatering of coal fines may be achieved via acombination of froth flotation separation, specifically designed forultrafines and microfine particles, plus mechanical and thermaldewatering techniques.

In all of the examples, the purified coal pellets used as a coalreplacement product are prepared by several process stages.:

A representative sample of coal waste slurry, e.g. Queenslandmedium-volatile bituminous coal A, derived from an impoundment, tailingspond or production tailings underflow is taken.

Particle Size Reduction

The sampled material is then reduced to a particle size of d80=30-50microns (or finer in some coals) to achieve efficient separation to atarget ash content of 5-8%. To achieve this, the feed is diluted withwater to achieve a solids content of in the range 20-40%, then ground ina ball or bead mill depending on the top size of the feed. The productis screened at a size range of approximately 100 microns. In somecircumstances a dispersant additive (e.g. lignin-based dispersants, suchas Borresperse, Ultrazine and Vanisperse manufactured by Borregaard,1701 Sarpsborg, Norway) is included to optimise energy use. Suitableequipment is manufactured by Metso Corporation, Fabianinkatu 9 A, PO Box1220, FI-00130 Helsinki, FIN-00101, Finland, Glencore Technology Pty.Ltd., Level 10, 160 Ann St, Brisbane QLD 4000, Australia, and FLSmidth,Vigerslev Allé 77, 2500 Valby, Denmark.

Ash Removal

Typically, one stage of flotation (one rougher and several cleanersteps) is carried out to bring the ash content down to the target level.For some coals where the mineral matter is disseminated mainly withinsub-10-micron size domains, more than one stage of flotation followingfurther milling may be required.

Purified coal has been manufactured from a range of coal waste feedsfrom impoundments, tailings ponds and production underflow destined forimpoundments and tailings ponds. These include coals from USA,Australia, South Africa and India of Carboniferous, Permian andCretaceous geological ages and coal rank ranging from low-volatilebituminous to sub-bituminous, see Table 1. Using feeds with ash contentsranging from 24% m to 70% m, milling to approximately 30 μm particlesize (d80) followed by cleaning stages leads to products withsignificantly lower ash contents, some as low as 5-10% m, but most from10-30% m ash. A second milling to approximately 10 μm particle size(d80) followed by cleaning stages leads to products with ash contents inthe range 0.6% m to 10.2% m, many of which have low enough ash contentsto be used as a low ash blending feed, Finally, a third milling toapproximately 5 μm particle size (d80) followed by cleaning stages leadsto purified products with ash contents in the exceptionally low range of0.7% m to 3.1% m,

In some instances, processed coal with ash contents ranging from 4.2% mto 10.2% m has also been purified in the same way. The resultant ashcontents of products at stage one were 1.2% m to 6.2% m, at stage two0.6% m to 3.7% m, and at stage three 0.2% m to 2.8% m.

Table 1 shows the properties of froth flotation feeds and cleanedproducts from stage 1, stage 2 and stage 3 for a range of coals ofdifferent rank, geographical origin, geological age and source type.Sub-bituminous coals such as row 12 and row 17 examples are lesshydrophobic than bituminous coals, which reduces the effectiveness ofseparation of hydrophilic and hydrophobic components by froth flotation.Recovery and separation in froth flotation is typically very poor forlow rank coals, so it was surprising that we were successful inobtaining modest, yet significant yields (32-47% m) of product with anash content as low as 2.3% m from a sub-bituminous coal.

TABLE 1 Properties of froth flotation feeds and cleaned products fromstage 1, stage 2 and stage 3 for a range of coals of different rank,geographical origin, geological age and source type. Froth FlotationFeed Sulphur content Volatile Vitrinite Vitrinite Ash Total Organic ASTMMatter reflectance content content (St) (So) St − So Source type classLocation Geological age % daf %* % v % m d.b. % m d.b. Impoundment hvbPA, USA Carboniferous 35.2 0.89 84 44 not determined Impoundment hvb KY,USA Carboniferous 33.0 0.74 69 45 1.31 0.40 0.91 Tailings ponds lvb QLD,Australia Permian 21.9 1.10 67 62 1.04 0.13 0.91 Tailings ponds hvb NSW,Austrlalia Permian 37.8 0.64 96 45 0.32 0.09 0.23 Tailings ponds hvcNSW, Australia Permian 35.8 0.58 73 59 not determined Tailings ponds hvbSouth Africa Permian 32.4 0.82 50 24 0.66 0.27 0.39 Underflow hvb WV,USA Carboniferous 42.2 0.75 not 70 4.09 n.d. Underflow hva WV, USACarboniferous 33.0 1.03 available 60 2.73 0.39 2.34 Underflow hvb WV,USA Carboniferous 35.9 0.99 52 1.47 0.32 1.15 Underflow hvb WV, USACarboniferous 33.0 0.89 62 61 0.41 0.11 0.30 Underflow sub CO, USACretaceous 42.0 0.68 81 39 0.49 n.d. Underflow hvb WV, USA Carboniferous38.6 0.74 82 48 3.00 2.06 0.94 Underflow hva WV, USA Carboniferous 42.60.78 80 45 3.30 n.d. Underflow hva KY, USA Carboniferous 35.9 0.91 82 520.82 0.49 0.33 Processed hva KY, USA Carboniferous 41.3 0.90 69 4.2 0.990.87 0.12 Processed sub AZ, USA Cretaceous 47.5 not determined 9.2 0.520.42 0.10 Processed hva AL, USA Carboniferous 30.6 1.10 78 10.4 0.600.46 0.14 Stage 2 Stage 3 Stage 1 Particle Ash Coal Particle Ash CoalSulphur content Particle Ash Coal Size content Yield Size content YieldTotal Organic Size content Yield μm % m d.b. % m μm % m d.b. % m (St)(So) St − So Source type μm % m d.b. % m μm % m d.b. % m μm % m d.b. % m% m d.b. Impoundment 38.0 7.1 89 8.6 3.0 88 4.5 1.4 88 0.81 0.73 0.08Impoundment 31.7 10.6 90 10.5 3.0 88 5.0 1.2 87 0.74 0.68 0.06 Tailingsponds 34.5 30.7 82 10.0 10.2 76 4.6 2.3 75 0.54 0.38 0.16 Tailings ponds26.8 13.6 66 9.8 3.1 63 4.8 0.6 58 0.48 0.45 0.03 Tailings ponds 31.517.3 79 10.4 6.7 75 5.8 1.6 67 not determined Tailings ponds 35.7 9.8 8610.9 2.9 83 5.1 1.0 80 0.43 0.37 0.06 Underflow 25.7 17.9 72 9.7 6.7 685.3 2.1 67 2.34 1.9 0.44 Underflow 23.9 11.0 85 8.6 7.1 83 4.5 2.4 821.04 0.74 0.30 Underflow 24.4 14.8 85 9.1 6.4 83 4.8 3.1 81 0.99 0.760.23 Underflow 23.0 21.4 66 9.8 6.0 63 4.8 1.7 59 0.79 0.73 0.06Underflow 35.0 14.3 52 10.2 7.3 45 4.8 2.3 32 0.61 0.54 0.07 Underflow33.0 6.5 86 10.7 3.0 81 5.1 0.8 72 1.51 1.47 0.04 Underflow 29.7 8.0 897.9 2.3 87 4.7 1.3 85 2.14 1.92 0.22 Underflow 32.2 4.6 88 8.6 1.7 835.0 0.7 73 0.83 0.78 0.05 Processed 34.7 1.2 94 9.5 0.6 92 5.1 0.2 840.87 0.78 0.09 Processed 30.2 4.4 72 10.1 3.0 65 5.0 2.3 47 0.68 0.580.10 Processed 28.6 6.2 99 8.5 3.7 99 4.8 2.8 98 0.57 0.51 0.06 lvb: lowvoaltile bituminous coal, hva: high volatile a bituminous, hvb: highvolatile b bituminous, sub: sub-bituminous *As vitrinite mean randomreflectance, unless shown in parentheses when it is given as vitrinitemean maximum reflectance n.d. not determined

The coal slurry is diluted further with water typically to a range of5-20% m solids then collected in a tank and froth flotation agents,known as frother (e.g. methyl iso-butyl carbinol and pine oil) andcollector (e.g. diesel fuel or other hydrocarbon oil, and Nasmin AP7from Nasaco International Co., Petite Rue 3, 1304 Cossonay,Switzerland), are added using controlled dose rates. Micro particleseparators (e.g. Flotation test machines manufactured by FLSmidth,Vigerslev Allé 77, 2500 Valby, Denmark, by Metso Corporation,Fabianinkatu 9 A, PO Box 1220, FI-00130 Helsinki, Finland, and GTEKMineral Technologies Co. Ltd.) filled with process water and filteredair from an enclosed air compressor are used to sort hydrophobic carbonmaterials from hydrophilic mineral materials. Froth containinghydro-carbonaceous particles overflows the tank and this froth iscollected in an open, top gutter. The mineral pulp is retained in theseparation tank until discharged, whereas the demineralised coal slurryis de-aerated, before being pumped to the pelletisation step.

Sulphur Removal

Table 1 also illustrates the impact of the process on sulphur removalfor the range of samples tested. Sulphur is found in coal as the mineralpyrite, as mineral sulphates and as organically-bound sulphur (e.g.native organic sulphur). Results are given for the total sulphur (St)and organic sulphur (So) of the feed and the thirds stage product. Inaddition, the difference between total sulphur and organic sulphurcontents (St−So), i.e. the mineral sulphur component, has been computed.The process removes only mineral sulphur, and not organic sulphur. It isremarkable how low the mineral sulphur component is in the third stageproducts, mostly within the 0.03-0.10% m range, though higher values arealso obtained up to 0.44% m. The higher values of (St−So) representsamples with significant amounts of sub-micron mineral domains. Incontrast the feed mineral sulphur content (St−So) values for theunderflow, impoundment and tailings pond feeds are much higher than thatfor most products, often greater than 0.9% m.

Dewatering

The concentrate from froth flotation is then dewatered with afilter-press or tube-press to a target range of 20-50% m depending onthe actual particle size, under pressure or vacuum, sometimes withair-blowing, to remove water by mechanical means, in order to generatefeed for the extruder. Suitable filter-press equipment is manufacturedby Metso, FI-00130 Helsinki, Finland, FLSmidth, Valby, Denmark, and byOutotec. Rauhalanpuisto 9, 02230 Espoo, Finland.

In some instances, flocculant (or thickener, e.g. anionic polyacrylamideadditive manufactured by Nalco Champion, 1 Ecolab Place, St. Paul, Minn.55102-2233, USA) is added to optimise settling properties and underflowdensity. To optimise the procedure settling tests are carried out tomeasure settling rates and generate a settling curve, tracking underflowdensity with time.

Filtration may also be necessary depending on the filtration rate andresultant cake moisture. To optimise the procedure feed % solids(thickened/un-thickened), feed viscosity, pH and filtration pressurewill be measured, Filter cloths are chosen after assessment of cakedischarge and blinding performance. Suitable filter cloths aremanufactured by Clear Edge Filtration, 11607 E 43rd Street North, Tulsa,Okla. 74116 USA.

In some circumstances a Decanter Centrifuge can be incorporated into theprocess design to concentrate the solids content prior to the filterpress. Suitable equipment is manufactured by Alfa Laval Corporate AB,Rudeboksvagen 1, SE-226 55 Lund, Sweden.

Additional Processing

The purified coal product may be utilised in micronized particulateform, for example in cases where the product is mixed into a liquid oilto form a solid-liquid blend.

If further processing to produce a pellet or briquette is required, anextruder is used to compact the wet cake of microfine coal into solidshaped articles to provide mechanical integrity. Suitable pelletisingextruder equipment is manufactured by Erich NETZSCH GmbH & Co. HoldingKG, Gebrüder-Netzsch-Straβe 19, 95100 Selb, Germany and by Bonnot Co.,1301 Home Avenue, Akron, Ohio 44310, USA.

The microfine coal wet cake is either fed to the extruder with orwithout an organic binder additive (such as starch, polyvinyl acetatepowder, molasses, gum Arabic, lignosulphonates, carnauba wax, guar gumetc.) which are mixed with the wet cake to optimise pelletisation. Themixture is forced under pressure through a die, typically containingseveral circular or lozenge-shaped holes which determine the pelletdiameter. The length of the pellets is then controlled by a simplecutting device.

Alternatively, a pin mixer or disc pelletiser can be used to form coalagglomerates. Suitable agglomerating equipment is manufactured by FeecoInt., 3913 Algoma Road, Green Bay, Wis. 54311-9707 USA

The microfine coal wet cake is fed with or without organic binder into apin mixer. The high-speed spinning action created by a single rotorshaft affixed with rods or pins thoroughly mixes the components andbegins to form agglomerates as the material moves through the length ofthe mixer.

The microfine coal wet cake is fed with or without organic binder into adisc pelletizer which tumbles the material onto a rotating disc, withorganic binding agent and feed being continuously added. The wet finesto become tacky and pick up additional fines as the material tumbles.Once pellets have coalesced to reach the desired size, uniform, roundpellets exit the rotating disc via centrifugal force.

Alternatively, a roll-type briquette machine can be used to compact thewetcake into moulded briquettes. Suitable briquetting equipment ismanufactured by K. R. Komarek Inc., 548 Clayton Ct., Wood Dale, Ill.60191, USA

The microfine coal wet cake is fed with or without an organic binder viaa simple gravity type feeder, screw or auger type feeder which controlsthe mass of material passing between the rolls. The wet-cake is squeezedby applying hydraulic pressure between two rolls rotating in oppositedirections, typically one roll is fixed, the other is moveable, butrestrained by hydraulic cylinders. Cavities or indentations cut into thesurfaces of the rolls form the briquettes.

Alternatively, a compression moulding briquette machine can be used tocompact the wetcake into moulded briquettes. Suitable briquettingequipment is manufactured by Ruf Maschinenbau GmbH & Co. KG, HausenerStr. 101, 86874 Zaisertshofen, Germany.

The microfine coal wet cake is loaded into the hopper of the briquettingmachine with or without an organic binder and transported into apre-charging chamber by a conveying screw. A pressing ram compresses thematerial into the mould and forms the briquette into its final shape anddensity. The reciprocating mould moves sideways and the briquette isejected as the next briquette is formed.

Drying

The PCP product or demineralised coal pellets (coal agglomerates or coalbriquettes) are then dried thermally to reduce water to below 5% m. byconveying them to a belt pellet dryer where oxygen-deprived hot processair is blown directly over the microfine coal pellets. Suitableequipment is manufactured by STELA Laxhuber GmbH, Öttingerstr. 2,D-84323 Massing, Germany or by GEA Group Aktiengesellschaft,Peter-Müller-St. 12, 40468 Düsseldorf, Germany).

The pellets/briquettes (PCP) are assessed in terms of their materialhandling properties via several standard tests, e.g. impact resistance,abrasion resistance, crush resistance and water resistance.

Example 1 Preparation of Purified Coal Pellets by Extrusion

A sample with an ash content of 52.6% m taken from the underflow rejectstream from a preparation plant processing a US medium-volatilebituminous coal was ground with a ball mill to achieve a grind size ofd₈₀ 36 μm (i.e. 80% of the particles are below 36 μm in diameter) andscreened at 100 μm. This was treated in a froth flotation apparatus witha few drops of MIBC as frother. Froth containing organic coal particleswas collected, de-aerated and dewatered to 50 and 60% moisture; theirresultant ash content was 7.6% m.

Using guar gum as binder, at proportions of 1.6, 4.0 1 nd 7.5% w/w,ultrafine coal was blended to form a slurry with a target viscosity ofapproximately 500,000 centipoises, then formed into pellets using anextruder manufactured by Netzsch. Pellets ranged from 10 to 25 mm indiameter, with lengths up to 50 mm. Feed slurry solids content rangedfrom 40 to 70% w/w. Pellets were then dried in an oven at 60-70° C.

Pellet assessment was conducted with tests for impact resistance andwater resistance.

-   -   Impact resistance was measured using a variant of ASTM D440        Standard Test Method of Drop Shatter Test for Coal by dropping        pellets from 2 m height on to a steel plate twice before        measuring the pellet fragments. A much smaller sample size than        the ASTM 440 recommended 23 kg was tested because insufficient        sample was available. Pellets were tested in duplicate.        Collected fragments were examined under a Zeiss Discovery.V8        stereo microscope and their size measured using Zeiss AxioVision        software. Each pellet broke into 20-30 fragments, with fragment        diameters ranging from 2 to 19 mm. The Ferret minimum diameters        of the fragments were measured, and Ferret minimum diameters        representing the sieve sizes specified in ASTM D440 were        selected in order to produce a simulated sieve particle        distribution of the fragments from PCP pellets prepared at        different guar gum concentrations, which is illustrated in FIG.        2(a).    -   Water resistance was assessed by submerging pellets in water for        up to 1 hour, with mass gain of the pellets measured and        integrity of the pellets reviewed every 10 minutes. Pellets were        dried and then a single test carried out at each concentration        of guar gum. FIG. 2(b) shows water uptake results for PCP        pellets at different guar gum concentrations.    -   The water resistance index was calculated (see for example        Richards, S. R., Physical testing of Fuel Briquettes, Fuel        Processing Technology, 25 (1990) 89-100):        -   WRI=100-% by mass of water gain after 30 minutes.        -   WRI values of 47% m, 63% m and 61% m were obtained for            concentrations of 1.6, 4.0 and 7.5.

Example 2 Blending of Waste-Derived PCP with Low Grade Native Feedstock

Metallurgical coking coal is heated in an oxygen deficient environmentto manufacture coke of sufficient strength and reactivity to be used asa reducing agent in smelting iron ore in a blast furnace. Specialproperties are required and the Australian Hard Coking Coal tradingspecifications are shown in Table 2 below (column 1). Coking coals havehigh value, approximately two times that of a high quality thermal coal.Furthermore, coking coals are in short supply globally.

Table 2 also shows the properties of a purified coal product (PCP)produced after upgrading two samples of waste derived during mining of amedium volatile bituminous coal A from Queensland, Australia: one takenfrom a tailings pond, the other from a coal processing plant thickenerunderflow waste stream. A thickener is a large circular tank that isused to dewater coal waste streams by enabling the solid material tosettle out from water. Thickened slurry is pumped out of the bottom ofthe tank and the resultant thickener underflow is disposed of by pumpingto a tailings pond or impoundment or other means.

TABLE 2 Upgrading of a Production Coal B to meet coking coalspecifications by blending with purified coal replacement product (PCP)manufactured from production waste (Coal A) Production Coal B AustralianQueensland Medium Volatile bituminous coal A 50% blended with CRP HardPonded Tailings Thickener Underflow 100% from from Coking Typical AsUpgraded As Upgraded unblended Ponded Thickener Coal spec productreceived to CRP received to CRP with CRP Tailings underflow ColumnNumber 1 2 3 4 5 6 7 8 9 Total Moisture % m, as received 10 9.5 14.1 2.041.2 2.0 12 7 7 Ash content % m, air dried 9.5 9.7 23.9 4.2 31.2 5.5 149.1 9.75 Total Sulphur content % m, air dried 0.6 0.6 n.d. 0.5 n.d. 0.50.7 0.6 0.6 Free Swelling Index, min 8 8.5 3.5 8 1 8.5 8 8 8.25 VolatileMatter content % m, air dried 23 21 18 23 17 23 22 22.5 22.5 GieselerFluidity max dial 1000 350 n.d. 300 n.d. 350 3000 949 1025 divisions/minPhosphorus content % m, air dried 0.05 0.035 0.035 0.035 0.06 0.04750.0475 n.d.—not determined

The properties of the waste streams themselves are shown in Table 2(columns 3 and 5) and a typical native coal product from this mine(column 2) are also given.

By producing the PCP as described above, it is possible to achieve aquality specification significantly higher than the native coal fromwhich it is derived. In this case, the ash, sulphur and moisturecontents of 4.2-5.5% m, 0.5% m and 2% m for PCP from ponded tailings(column 4) and thickener underflow (column 6) respectively comparefavourably with ash, sulphur and moisture contents of 9.7% m, 0.6% m and9.5% m respectively for the typical production coal A (column 2). SuchPCP meets all the specifications for Australian Hard Coking Coalexcepting Gieseler fluidity (a measure of thermoplasticity) and,consequently, could be traded in the same way as the typical productcoal A. Hence, by processing thickener underflow and/or ponded tailingsto PCP, the production of high value coking coal A from this site can beincreased significantly via increased efficiency of coal extraction.

A production coal B (column 7) exceeds the required specifications ofAustralian Hard Coking Coal (column 1) for several parameters, i.e. ash,sulphur, phosphorus and moisture contents. When coal B is blendedequally (1:1) by mass with PCP manufactured from ponded tailings (column8) or thickener underflow (column 9)—referred to as coal replacementproduct (CRP)—then all the specification parameters of the resultantblend meet the Australian Hard Coking Coal specification (column 1).

Example 3

Purified coal pellets can also be manufactured from high ash contentinferior seam coal, hitherto not exploitable economically. An example ofsuch coal is the Late Permian Fort Cooper Coal Measures (FCCM), whichform a sequence of 400-450 metres (gross thickness) throughout the BowenBasin in Queensland, Australia. FCCM comprises coal seams interbeddedwith mineral tuffs and carbonaceous mudstone, and are subdivided into anupper Burngrove Formation, a lower Fair Hill Formation and a series ofMiddle Main Seams, including the Black Alley Shale (Ayaz, S. A.,Rodrigues, S., Golding, S. D., Esterle, J. S., Compositional variationand palaeoenvironment of the volcanolithic Fort Cooper Coal Measures,Bowen Basin, Australia, International Journal of Coal Geology (2016),doi:10.1016/j.coal.2016.04.). These are high vitrinite-containing thickseams, typically >70% by volume, occurring in the same geologicalsequence and location as coking coal production mines (Permana, A. K.,Ward C. R. and Gurba, L. W., Maceral Characteristics and VitriniteReflectance Variation of The High Rank Coals, South Walker Creek, BowenBasin, Australia, Indonesian Journal of Geology, Vol. 8 No. 2 June 2013:63-74, http://oaji.net/articles/2014/1150-1408500933.pdf)., neverthelessare uneconomic to process using conventional coal preparation methods,because of their ash contents are so high, in the range 40-60% m.

Feed samples derived from the FCCM measures in Queensland, Australiawere screened at 1.7 mm size and the oversize crushed until it passesthe 1.7 mm screen, then both <1.7 mm samples combined, blended and splitinto sub-samples. A sub-sample with an ash content of 60.6% m dry basiswas ground and separated in a float cell by several stages of grindingand dilution cleaning at successive particle sizes of d₈₀=˜40 μm (test1A), d₈₀=˜15 μm (test 1B), d₈₀=˜10 μm (test 1C) and d₈₀=˜5 μm (test 1D).The results are given in the Table below. A second sample with an ashcontent of 75.4% m dry basis was treated similarly cleaning atsuccessive particle sizes of d₈₀=˜30 μm (test 2A), d₈₀=˜6 μm (test 2B),d₈₀=˜5 μm (test 2C).

Thus, purified coal with ash contents below 5% m have been prepared withmoderate (1^(st) sample) and very high (2^(nd) sample) coal yields.Higher yields were obtained for the first sample at d80 values of 11 and15 μm with ash contents of approximately 8% m. Such samples have lowsulphur content (0.55-0.79% m) and show significant swelling properties(CSN 4-6).

TABLE 3 Yield and Analytical properties of purified coal fractionsseparated from coal waste using a successive grinding and dilution frothflotation technique. Sulphur Particle Ash content content Crucible YieldTest size (%, dry (%, dry Swelling No. (% dry No. (d₈₀) basis) basis)(CSN) coal basis) 1^(st) FCCM sample: Ash content of feed = 60.6% m drybasis 1A 43 13.9 n.d. 4.5 42 1B 15 7.6 0.79 6 43 1C 11 8.1 0.75 4 56 1D4.6 2.0 0.55 n.d. 36 2^(nd) FCCM sample: Ash content of feed = 75.4% mdry basis 2A 31 24.7 n.d. 78 2B 5.6 8.5 76 2C 4.9 3.5 75 Indian coalsample 1: Ash content of feed = 49.2% m dry basis 3A 20.9 17.0 n.d. 923B 9.9 9.0 87 3C 4.3 4.6 84

A sample of an Indian Permian age coal from Jharkhand state with an ashcontent of 49.2% m dry basis was treated similarly cleaning atsuccessive particle sizes of d₈₀=˜20 μm (test 3A), d₈₀=˜10 μm (test 3B),d₈₀=˜5 μm (test 3C). High (>80% m) coal yields were obtained at bothd₈₀=˜10 μm with ash content of just 9% m, and at d₈₀=˜5 μm with an ashcontent below 5%.

TABLE 4 Petrographic properties of purified coal fractions separatedfrom coal waste using a successive grinding and dilution froth flotationtechnique Vitrinite Random Vitrinite Liptinite Inertinite SampleReflectance (%) (% vol) (% vol) (% vol) 2C 0.95 83 0 17 3C 0.88 60 0 40

The vitrinite random reflectance values show that both coals were highvolatile bituminous coals close to the coking coal range.

A. Pulverised Coal Injection (PCI)—Blending of PCPs

Pulverized Coal Injection (PCI) provides a supplemental carbon sourceinto a blast furnace to speed up the production of metallic iron,reducing the need for coke production. As a result, energy use andemissions can be reduced. Such coals have special property requirementsand high value: typically, approximately 50% more that of a high qualitythermal coal.

Table 5 below shows the properties of PCP produced after upgrading asemi-anthracite from a South Wales waste tip (coal C) and a low-volatilebituminous coal from a US impoundment (coal D).

TABLE 5 Blending PCP from South Wales waste (coal C) and US waste (coalD) to meet PCI specifications South Wales Coal C US Coal D Typical Asreceived As received 50% blend of PCI from waste Upgraded from coalUpgraded CRPs from Coal Coal property Units specs tip to CRP impoundmentto CRP C and Coal D Column Number 1 2 3 4 5 6 Moisture content 8-9 21.52 25 1.9 2 Ash content % air dried  8-10 63.9 3.6 26 8.8 6 Total Sulphurcontent % air dried 0.4-0.6 n.d. 0.7 n.d. 0.5 0.6 Net Calorific Value asreceived 7000   2520 8220 7720 7970 Phosphorus content % air dried0.04-0.08 n.d. 0.1 0.01 0.055 Volatile Matter content % air dried 14-1611 18.2 15 n.d. not determined

The properties of the waste streams themselves (columns 2 and 4), theupgraded PCP coal replacement product from each waste (columns 3 and 4),and an example of typical PCI trading specifications (column 1) aregiven. The resultant PCPs have properties close to the required PCIspecification, except that the South Wales coal has sulphur andphosphorus content that is slightly too high for PCI use, and neitherPCP fits the optimum volatile matter range. By mixing the two PCPsequally (1:1) by mass (column 6) the resultant blend properties all meetthe PCI specification (column 1). Consequently, coal waste has beenupgraded not only to a quality utilisable as thermal coal (Table 4), butto a higher value PCI coal product by blending from sources of differentcoal rank and quality.

B. Thermal Coals

Thermal coals are mainly used for power generation and are tradedinternationally according to regionally agreed specifications. Two suchAustralian trading specifications, one for Japan (column 1) and one forChina (column 2), are shown in Table 6 below. Thermal coal for Chinatrades typically at about US$20/tonne less than that for China, itslower price reflecting the lower quality requirements for ash contentand calorific value.

TABLE 6 Increasing production of international thermal coal E bymanufacturing PCP from thickener underflow waste Coal processed fromseam F 50% blended Australian Thermal NSWThermal Coal E with CRP Coalspecs Thickener Underflow 100% from for for Typical As Upgradedunblended Thickener Coal property Units Japan China product received toCRP with CRP underflow Column Number 1 2 3 4 5 6 7 Total Moisture % max,as received 15 15 9 66 2.0 20 11 Ash content % max, air dried 15 24 9-12 52 3.8 26 14.9 Total Sulphur content % max, air dried 0.75 0.75  0.6 n.d. 0.5 0.9 0.7 Net Calorific Value kcal/kg, min 6000 55006900-7150 2300 7580 5000 6290 n.a.—not available, n.d.—not determinedFigures in parentheses are for Gross Calorific Value

Table 6 shows the properties of PCP coal replacement product producedafter upgrading high volatile bituminous coal from NSW, Australia, takenfrom a coal processing plant thickener underflow waste stream (column5). The properties of the waste stream (column 4) and a typical product(column 3) from this mine are also given. Both the typical product coalE and the upgraded PCP meet both Australian specifications for Japan andChina. Hence, by processing thickener underflow waste to PCP, theproduction of coal E from this site can be increased via increasedefficiency of coal extraction.

After processing another coal seam, coal F, from this site gives lowerquality than that required by either the Japanese or the ChineseAustralian specifications: shortfalls in ash, moisture and sulphurcontents, as well as calorific value (column 6) are obtained. Ifprocessed coal F is blended equally (1:1) by mass with PCP manufacturedfrom waste coal E thickener underflow (column 7), then all thespecification parameters of the resultant blend meet the Australianspecifications for both Japan and China. Hence, by processing thickenerunderflow to PCP, the production of internationally tradeable coal fromthis site can be increased by including an additional coal seam ofinferior quality on its own.

Example 4

US North Appalachian Thermal Coal trading specifications are given inTable 7 below (column 1).

Table 7 also shows the properties of PCP coal replacement productproduced after upgrading high volatile bituminous coal from Kentucky,USA, coal G, taken from a coal impoundment (column 4). The properties ofthe waste stream (column 3) and a typical product (column 2) from thismining area are also given. The typical product coal and the upgradedPCP now meet both US North Appalachia specifications for thermal coal.Hence by processing coal waste stored in an impoundment to PCP, aproduct fit for use as a traded thermal coal can be produced.

TABLE 7 Upgrading coal impoundment waste to internationally tradeablethermal coal by manufacturing PCP of sufficient quality to upgrade alower quality coal resource US Appalacian Coal G Coal H US North TypicalCentral Impoundment 100% 50% blend Appalacia Appalacia As Upgradedunblended with CRP from Coal property Units specs product received toCRP with CRP impoundment Column number 1 2 3 4 5 6 Total Moisture % max,as received 15 5 60 2.0 24 13 Ash content % max, air dried 8 8 47 4.9 107.5 Total Sulphur content 2 1.2 n.d. 0.9 3.0 1.95 Volatile Mattercontent 35 33 33.5 36.5 35.0 Net Calorific Value kcal/kg, min, as 67007200 1600 7650 5800 6725 received n.a.—not available, n.d.—notdetermined Figures in parentheses are for Gross Calorific Value

After processing, a coal (coal H) from another mining site gives lowerquality than that required by US North Appalachian thermal coalspecifications: shortfalls in ash, moisture, volatile matter and sulphurcontent, as well as calorific value (column 5) are obtained. If coal His blended equally (1:1) by mass with PCP manufactured from coal Gimpoundment (column 6), then all the specification parameters of theresultant blend meet the US North Appalachian thermal coalspecifications. Hence, by blending PCP from coal impoundment waste, acoal of inferior quality on its own can be upgraded to internationallytradeable coal standards.

Example 5

Blending Purified Coal Pellets into Coal Pulveriser Feed for PowerGeneration

Because of the complexities of a large coal-fired power plant, computermodels have been developed to evaluate the technical and economicimpacts of fuel quality changes based on operating experience. One suchmodel is the Fuel Evaluation Tool developed by Uniper Technologies(www.uniper.energy—Uniper SE, Dusseldorf, Germany) which has been usedto evaluate quantitatively the advantages of the purified coal productpellets (PCP) described herein. The entire power generation process ismodelled, including fuel purchase and delivery, utilisation within theplant including impacts on efficiency, maintenance and availability,emissions, reagents and by-products. The Fuel Evaluation Tool is able toaccount for performance impacts on a typical modern power plantresulting from fuel quality changes.

Purified coal replacement product (Ash content 4.3%, Moisture 2.0%,Volatile Matter 35.8% Gross Calorific Value 33.2 MJ/kg, total Sulphur0.8%, Chlorine 0.05%—all as received basis) has been evaluated for fourpower plant configurations typical for different regions, i.e. USA,Germany and two for India and compared with a variety of typicallytraded coal feeds from USA (Illinois, Appalachian and Powder RiverBasin), Colombia, Russia, South Africa, Indonesia and India; each powerplant configuration is described by around 200 user inputs, the mostimportant parameters for each power plant are shown in Table 8.

TABLE 8 Main model parameters for different Power Plant configurationsUS German Indian Indian Coal Coal Coal Coal Total Power Capacity, MW 600530 600 660 Sent Out Power Capacity, MW 535 500 555 614 Gross UnitEfficiency, % 36.3 40.1 34.6 38.5 Net Unit Efficiency, % 38.0 42.1 37.040.8 Annual Generation, GWh 2000 1752 3645 4030 Capacity Factor, % 40%40% 75% 75% Equivalent Availability, % 91.0 90.0 84.0 90.0 LostGeneration Cost, $/MWh 12.0 12.0 10.0 10.0 Ops & Maintenance, $/MWh 2.52.7 2.2 Design Coal US South Indian Indian Illinois African G-13 G-10Number of coal mills installed 6 4 8 6 Capacity of each coal mill, t/h45 45 58 65 Mill safety systems Expl. Sup- Expl. Sup- vents pressionvents pression Boiler NO_(x) produced, mg/Nm³ 650 440 650 650 SelectiveCatalytic Reduction Yes Yes No No NO_(x) emissions, mg/Nm³/removal 80%200 — — Electrostatic Precipitator installed Yes Yes Yes Yes ParticulateMatter limit mg/Nm³ 10 15 150 150 Flue Gas Desulphurisation installedYes Yes No No SO₂ emissions, mg/Nm³/removal 92% 200 — —

Total power plant (unit) efficiency is mainly determined by three of thefactors previously discussed: boiler efficiency, auxiliary power demandand steam temperatures (turbine efficiency). It has been shown that PCPis will have a beneficial impact on both boiler efficiency and auxiliarypower demand, and that this will result in higher unit efficiency whenfiring the pellets. FIG. 3 shows the calculated efficiency for theGerman hard coal power plant (NCV unit efficiency is shown). Thesignificant improvement in unit efficiency compared with Colombian,Russian, US high sulphur and South African coals leads to a directreduction in coal consumption per MWh of electricity generated. Thisdelivers cost savings and CO₂ reduction through the entire powergeneration process.

Improving coal quality will also deliver reductions in plant maintenancerequirements. Wear and tear within the coal plant and milling systemswill be much improved, as fewer tonnes of coal are required per unitelectricity production, and because PCP and PCP containing blends are aconsistent high-quality fuel. It is also fairly common for some coals tobe contaminated with tramp materials, such as rocks or metals. Thesetramp materials can have a disproportionate effect on wear rates,especially within mills. Operations and maintenance savings are alsoexpected for the Flue Gas Desulphurisation plant, where fewer tonnes ofreagent and by-product need to be processed. Likewise, costs for ashhandling will be significantly reduced for PCP, e.g. the number oflorries moving ash from the power plant to the end-user or disposal sitewill be greatly reduced.

Unit availability refers to the ability to deliver electricity to thegrid when demanded. If a problem occurs on plant the unit may need tocompletely shut down for repair (a ‘forced outage’) or the unit maycontinue operating, but at reduced power output (‘forced derate’). Bothinstances represent a loss of availability, and there is usually a costassociated with this, since the opportunity to make money by sellingpower is lost. In the four studies performed using the Fuel EvaluationTool a number of major technical problems have been highlighted whichwould lead to availability losses for the power plant concerned. PCP isexpected to lead to lower rates of forced derate and forced outage. Theplant areas where unit availability is expected to be improved are formills, boiler (lower tube failure due to corrosion, erosion, sootblowererosion etc), ash handling plant and FGD plant.

Although particular embodiments of the invention have been disclosedherein in detail, this has been done by way of example and for thepurposes of illustration only. The aforementioned embodiments are notintended to be limiting with respect to the scope of the invention. Itis contemplated by the inventors that various substitutions,alterations, and modifications may be made to the invention withoutdeparting from the spirit and scope of the invention.

1.-15. (canceled)
 16. A process for preparation of a purified coalproduct, the process comprising the steps of: a. obtaining a startingmaterial that comprises coal, and wherein the coal comprises a feedstockselected from one or more of the group consisting of: waste from coaltailings ponds, impoundments or tips; reject materials from coalproduction processing; and inferior coal; b. subjecting the startingmaterial to at least one fine grinding stage so as to reduce thestarting material to a particulate composition in which substantiallyall of the particles are no more than 500 microns (μm) in diameter; c.exposing the particulate composition to at least one froth flotationstage so as to separate hydrocarbonaceous material comprised within theparticulate composition from mineral matter, wherein during the at leastone froth flotation stage the hydrocarbonaceous material is associatedwith froth produced and separated from the at least one froth flotationstage, and wherein the froth flotation stage is conducted with solids toliquids loading of less than 20% m; d. washing the froth separated fromthe at least one froth flotation stage with water to release thehydrocarbonaceous material; and e. subjecting the hydrocarbonaceousmaterial to at least one dewatering stage so as to obtain a particulatepurified coal product that has an ash content of less than 5% m, a watercontent of less than 25% m and wherein the particles comprised withinthe particulate purified coal product have a d90 of less than 100 μm.17. (canceled)
 18. The process of claim 16, wherein the fine grindingstage is conducted in a ball or bead mill.
 19. The process of claim 16,wherein the froth flotation stage is conducted with solids to liquidsloading of less than 15% m.
 20. The process of claim 16, wherein thedewatering stage comprises subjecting the hydrocarbonaceous material todewatering selected from one or more of the group consisting of:mechanical dewatering; cyclonic dewatering; centrifugal dewatering; andthermal dewatering.
 21. The process of claim 16, wherein the particulatepurified coal product obtainable by the process has an ash content ofless than 2% m.
 22. The process of claim 16, wherein the particulatepurified coal product obtained by the process has a water content ofless than 20% m.
 23. The process of claim 16, wherein the particlescomprised within the particulate purified coal product have a d90 ofless than 50 μm.
 24. A particulate coal product obtainable by theprocess of claim 16, wherein the particulate purified coal product hasan ash content of <2% m, a water content of <7% m and wherein theparticles comprised within the particulate purified coal product have ad90 of less than 50 μm.
 25. The particulate coal product of claim 24,wherein the product is formed into a briquette. 26-27. (canceled) 28.The process of claim 16, wherein the froth floatation stage is conductedwith a solids to liquid loading of less than 10% m.
 29. The process ofclaim 16, wherein the froth floatation stage is conducted with a solidsto liquid loading of less than 5% m.
 30. The process of claim 16,wherein the particulate purified coal product obtained by the processhas a water content of less than 10% m.